It is possible to use texture atlases like button?

Sorry my bad English. I’m using this texture packer tutorial:here
I want to change the textures on button but I can not. Is there an example of use? I am looking to optimize my game reducing call draws and saw that texture atlas is a good option.

You can use a variable of type GUIStyle
Then set this variable using the packer

The list of properties of the style is : GUI Style